Question

One of the firm's suppliers discounts prices for larger quantities.
The first 1000 parts are $13 each. The next 2000 are $12 each. All
parts in excess of 3000 cost $11 each. What are the average cost
and marginal cost per part for the following quantities.
A. 500
B.1500
C.2500
D.3500
If you could show your calculations it would be very helpful.